The present invention relates to an apparatus for surface analysis of a recording surface. In particular, it relates to an apparatus for measuring head-disk contact using piezoelectric glidehead sensors. Most particularly, the present invention relates to piezoelectric sensors which are formed using microcircuit fabrication methods.
In a conventional magnetic storage drive, an air bearing slider supports a magnetic transducer in close proximity to a moving recording surface. Typically, the recording surface comprises a rigid disk coated with a layer of magnetic material. To assure long-term reliability and integrity the coated disks must be free of surface asperities at the head/disk interface. This is critical because asperities may lead to undesirable head/disk contact or "head crash".
One method of assuring that the disk surface contains no asperities is glide height testing. A slider is flown over the recording disk at a height equal to or below the desired head fly height to analyze impacts between the slider and the disk surface. The present art includes one or more piezoelectric sensors bonded to the slider on an upper surface facing away from the recording surface or bonded onto a "wing" which extends off to the side of the slider. Piezoelectric materials are used because they generate an electric charge in response to stress. As the slider experiences rigid body displacement and flexing deformation, the sensors respond by generating an electric signal which may be monitored.
During the glide test process, the glide head flies over the disk surface at a predetermined clearance from the disk surface, also known as glide height. If contact occurs between the glidehead and a disk asperity or defect, the glidehead is subject to vibration and deformation. The slider deformation results in a piezoelectric sensor (also known as a piezoelectric transducer ("PZT")) deformation. The PZT deformation produces a measurable electric signal which is carried by the electrodes of the PZT to a signal processor. When contact occurs, many vibrational modes of the PZT and slider are excited simultaneously, and each mode generates a voltage at its specific frequency. Typically, these signals are filtered and analyzed. If the magnitude of the analyzed signal exceeds a predetermined threshold level, the disk is rejected.
In recent years, the disk drive industry has been producing storage systems with smaller sliders than the conventional "100%" slider size (e.g., approximately 4 mm long by 3 mm wide). These reductions in slider size (e.g. 70%, 50%, 30%) necessitate a corresponding reduction in the test slider dimensions for an equivalent compliance to the recording surface. Unfortunately, existing PZT's are quite large with respect to the smaller sliders. The excessive weight and size of the PZT sensors causes the results obtained in glide height testing to vary substantially from actual slider performance (i.e., sliders without a PZT sensor). The large size of current PZT sensors causes torquing and imbalances when placed on a wing and causes significant dynamic variations when placed directly over the glidehead. Significantly, the present technology does not produce accurate readings for glideheads smaller than 50%.
Others have recently succeeded in fabricating small ZnO sensors on glideheads. (Imai, et al. JSME International Journal, Series C, Vol. 40, No. 1, 1997). However, these sensors are separately prefabricated and subsequently placed on a silicon glidehead. It is one objective of the present invention to radically reduce the size of the piezoelectric sensors used to measure vibrations induced by disk surface asperities. A further object of the invention is to fabricate the sensor of the present invention directly into Al.sub.2 O.sub.3.TiC glideheads. By reducing the size of the sensors and fabricating directly on top of the glidehead, the present invention can be used on smaller glideheads than present technologies and dispense with the need to have a wing on the glidehead. Another objective of the present invention is to adapt microchip fabrication techniques to sensor fabrication. Another object of the present invention is to provide a sensor configuration which delivers an optimal signal to noise ratio and provides the greatest amount of information regarding slider vibration. The radically reduced size of the sensors of the present invention do not significantly alter glidehead performance of reduced size glideheads as does the current art. The present invention provides a small apparatus for analyzing the disk surface for the presence of asperities without significantly altering the vibrational and resonance characteristics of the glidehead.